The work described herein consists of a detailed examination by cDNA hybridization of the kinetics of accumulation and disappearance of vitellogenin mRNA in rooster liver following both primary and secondary injections of 17 beta-estradiol. It has been demonstrated that the enhanced vitellogenic response following secondary treatment with the hormone as compared with that following primary stimulation can be attributed to a more rapid and extensive accumulation of vitellogenin mRNA and does not stem from more efficient translation of the mRNA. Purified vitellogenin cDNA and mRNA have been used to examine the genomic organization of the vitellogenin gene. The results indicate that the gene may be composed of as many as 25,000 base pairs, while the cytoplasmic form of vitellogenin mRNA is only 7000 nucleotides long. Vitellogenin mRNA has been transcribed into double-stranded cDNA and this DNA has been inserted into the plasmid PBR322 and cloned in E. coli X1776. More than 100 clones containing vitellogenin DNA sequences have been isolated.